@Article{EcherSchuMakiOkan:2004:ObBrSo,
               author = "Echer, Ezequiel and Schuch, Nelson Jorge and Makita, K. and Okano, 
                         S.",
          affiliation = "{Instituto Nacional de Pesquisas Espaciais} and Centro Regional 
                         Sul de Pesquisas Espaciais, CRSPE/INPE and {Takushoku University - 
                         Tokyo} and National Institute of Polar Research, Tokyo",
                title = "Observations of broadband solar UV-A irradiance at Santa Maria, 
                         Brazil (29°S, 53° W)",
              journal = "Geof{\'{\i}}sica Internacional",
                 year = "2004",
               volume = "43",
               number = "1",
                pages = "53--59",
                month = "Jan.-Mar.",
             keywords = "Solar radiation, solar UV, atmosphere, atmospheric radiative 
                         transfer.",
             abstract = "Observations of broadband solar UV-A irradiance (320-400 nm) were 
                         made at Santa Maria, Brazil (29° S, 53° W) between September 1993 
                         and December 1996. Two different measurement techniques were used, 
                         the direct sun (DS) with the sensor pointed directly to the sun, 
                         and the zenith sky (ZS), with the sensor pointed to the zenith. 
                         The seasonal variation of UV-A DS and ZS irradiances measured at 
                         local noon is analysed. Both UV-A DS and ZS irradiances have a 
                         strong seasonal variability, anticorrelated to the solar zenith 
                         angle variation. It is shown that UV-A ZS irradiance has a larger 
                         seasonal variation than UV-A DS irradiance, with summer/winter 
                         ratios of 3.4 for UV-A ZS and 1.4 for UV-A DS. This difference is 
                         explained because of the geometrical arrangement of the 
                         observations; UV-A DS irradiance is easured tracking the sun and 
                         its variability is due to the atmospheric optical path variation 
                         during the year. UV-A ZS irradiance is diffuse irradiance measured 
                         pointing at a fixed direction, the zenith, and besides the 
                         atmospheric optical path variability, the component of direct 
                         irradiance incident on the horizontal surface has also a variation 
                         with solar zenith angle. Analysing UV-A DS and ZS irradiances 
                         versus solar zenith angle, it was observed that UV-A ZS decreases 
                         faster with higher solar zenith angles than UV-A DS. Calculations 
                         using Beers law at 370 nm were made and show similar behaviour for 
                         irradiances at a horizontal surface, compared to UV-A ZS, and at a 
                         surface perpendicular to the solar beam, compared to UV-A DS 
                         irradiance.",
           copyholder = "SID/SCD",
                 issn = "0016-7169",
             language = "en",
           targetfile = "Echer1.pdf",
        urlaccessdate = "12 maio 2024"
}